The thing is, the US have 91 AKI as the highest Octane available right ? And the car is manufactured in the US .. Doesn't that mean the car is built to withstand 91 Octane (95 RON) as the highest rating ? Which means anything after that doesn't really make much of a difference ?

The higher RON is preferable, coz you will never know the actual RON rating of the fuel in the petrol station. They may advertise as RON 98, but overtime during storage, the octane in the fuel will evaporate and this will in turn lower the rating of the fuel.

The SRT's engine management can adapt to the fuel change.. so, don worry. You just need to fill the car up with your desired fuel and just drive it like usual.

Hey guys I will never again use 95 after my last tank of 95. I had to put a tank of 95 in last week (as that's all my local station had) and after about 10 min or less of driving I could notice a massive drop in performance , I'd say probably 10 - 20%( not kidding ). So all week it's been in the back of my mind until this morning when I done a launch of 5.4 to 100kph whereas my previous average was 4.8 (as low as 4.6) stock. The biggest thing I found was that it just didn't want to kick down as quick or just seem as keen to get moving. Anyway that's my 2 cents. I'll be filling her up with no less than 98 as soon as this sydney weather stops (she only had a clay bath and polish yesterday arvo).